Very high cycle fatigue behaviour of S690 structural steel

Testing beyond 10 millions of cycles in a conventional fatigue machine is a very time consuming task, so the fatigue limit has been settled around this number of cycles. However, during the service life, several engineering components experience a number of cycles larger than 10 million cycles. For that reason, the region of very high cycle fatigue (VHCF), and the concept of fatigue limit has been matter of study and interest in the last decades. In order to overcome the time effort required, ultrasonic fatigue testing machine has being developed and widely used. Nevertheless, ultrasonic testing system and the VHCF region brought new challenges such as the frequency effect and the internal crack initiation. Thus, this research work intends to characterize the fatigue behaviour of S690 structural steel in the VHCF region. An experimental campaign of twenty specimens was performed in ultrasonic testing machine at a frequency of 20 kHz and a mean curve was determined. This work also approaches a design methodology of smooth fatigue specimens to be tested in ultrasonic fatigue machine.